This invention relates to the testing of the adherence of a coating to a sheet of material.
Various types of coatings are used extensively in the electronics and metal fabrication industries to protect or prime a metal surface. The coatings can be applied by controlled oxidation methods, glow discharge, electrodeposition, sputtering and painting. Irrespective of the nature of the coating and the metal surface, an important concern is the adherence of the coating to the metal substrate. Poor adherence almost invariably results in poor product. An example of an area where the proper adherence of an oxide coating to a metal substrate is important is the blackening oxide coating which is applied to the aluminum-killed steel used for shadow masks in cathode ray tubes.
Testing procedures presently available for testing adherence are not fully satisfactory. Typically, in the existing test procedure an element is affixed to the coated material using an epoxy or some other adhesive. The element is then pulled free from the substrate and microscopically examined to determine whether the element broke free from the coating, or whether the coating broke from the substrate. This type of testing is very sensitive to the angle of pull and the pull rate, the coverage area of the epoxy, and in the case of a poorly adhering coating, the epoxy can penetrate the coating and adhere directly to the metal substrate. For these reasons the test is not completely reliable for accurately determining the adherence of an oxide coating to a metallic substrate. There therefore is a need for a device for testing the adherence of a coating layer to a material substrate. The present invention fulfills this need.